Popular Science Monthly 



tween the rotating and fixed electrodes of 

 the rotary gap. If the studs are set back 

 so that when the gap is the shortest (i.e., 

 when the electrodes are exactly in line) 

 a voltage of 7,500 is required to cause a 

 spark to jump, and if the design is such 

 that a potential of 15,000 volts would 

 force a spark across even when the elec- 

 trodes are farthest apart (the moving 

 studs exactly half-way between the fixed), 

 the conditions illustrated in Fig. 42 will 

 be had. The spark gap is supposed to 

 have the number of studs and the speed 

 chosen so that the electrodes approach 

 and recede 600 times per second. The 

 illustration Fig. 42 shows roughly what 

 will happen in four half-cycles under these 

 conditions. The first time the gap be- 

 comes closest there will not be enough po- 

 tential to break it down, so the spark will 

 be missed. The second time udll produce 

 a spark, since the secondary condenser 

 will just have reached 7,500 volts. The 

 third spark will pass, as will the fourth. 

 These are indicated by shaded portions 

 where the two voltage curves overlap. 

 The fifth and sixth sparking opportuni- 

 ties will be missed, because the condenser 

 voltage will in neither case be high enough 

 to break across the minimum gap length. 

 At the seventh, eighth and ninth oppor- 

 tunity sparks will occur, and the tenth and 

 eleventh will miss. The twelfth, thirteenth 

 and fourteenth will pass, but the fifteenth 

 and sixteenth wall be lost. Thus it is seen 

 that there will be three sparks in each 

 half-cycle, at the distance represented by 

 1/600 second of time, and that between 

 each group of three sparks there will be 

 an idle interval of 1/200 (3/600) 

 second. If the sparking opportunities do 

 not occur at exactly 1/600 second separa- 

 tion, but slightly less often, there will be 

 two sparks in some half-cycles and three 

 in others. 



This will give a fairly complete idea of 

 the rotary gap operating upon the non- 

 synchronous principle. You should go 

 over the details of this type of non- 

 synchronous gap operations until you 

 have firmly in mind the relations of 

 voltage and gap length. The effect of 

 changing various adjustments will be 

 treated next month, when the quenched 

 and rotary synchronous gaps will also be 

 described. 



{To be continued.) 



709 



IIow to Make an Efficient Weather- 

 proof Goose-Neck 



AVERY efl'icient weather-proof goose- 

 neck wall bracket can be easily con- 

 structed as shown in the illustration. It 

 consists of a piece of ,' 2-in. conduit bent 



iSHirSG 



WOOD 

 BLOCK 

 LOCKNUT 



. pie: PLrtTEL- 

 GUTLEIT 

 BOX e>U5MlNG 



A conduit bent and fitted with pie- plate 

 reflector to make a weather-proof goose-neck 



in the shape shown and fastened into the 

 wall with a locknut. The outer end has a 

 wood block or disk attached with a lock- 

 nut and rubber gasket. On the under 

 side of this disk is an inverted pie plate 

 to which the lamp sockets are securely 

 attached. — Chris. Bach, Jr. 



A Temporary Repair for a Slipping 

 Magneto Shaft 



ABOUT the most annoying mishap a 

 L driver has to contend with on the 

 road is that of a magneto shaft slipping 

 endways so that the gears will be out of 

 mesh. One cause of this trouble is the 

 pump wheel shearing its pin and allowing 

 the shaft to slip endways and out of 

 mesh with the gears. In order to take 

 the pump off and make the repair it is 

 necessary to remove the starter, and this 

 is entirely too big a job to do on the road. 



TIMING GEARJ 



|GLAND*(STUFFING Noxf, 

 COTTER 



^z'hole. DRILLE.0 ^ 



-WATER PUMP 



Placing a cotter in a magneto shaft to keep 

 it from shifting endways out of gear mesh 



The repair may be made in a temporary 

 manner as shown in the illustration. A 

 hole drilled through the shaft just in 

 front of the stuffing box, as shown at A, 

 provides a way for holding the shaft with 

 a cotter. It is then only necessary to time 

 the distributor, and the engine runs the 

 same as before. — P. P. Avery. 



